1. Field of the Invention
The present invention relates to relates to semiconductor fabrication, and in particular to an interconnect structure with improved adhesion between a low-k dielectric layer and a diffusion barrier layer therein.
2. Description of the Related Art
Electrically conductive lines for tasks such as signal transferring are essential in electronic devices as well as in semiconductor integrated circuit (IC) devices. The electrically conductive lines on different levels are connected by electrically conductive plugs in required positions and provide predetermined functions.
Recently, fabrication using copper has been introduced to solve problems such as RC delay caused by device feature size reduction responding to demands of increased device integrity. Moreover, copper also shows better heat conductivity, thus providing better electromigration resistance than conventional aluminum. Copper fabrication compatible with low dielectric constant (low-k) dielectric material has become a leading interconnect process in the IC industry.
In the copper fabrication, a metal barrier layer comprising material such as Ta or TaN is needed and formed between the copper and adjacent low-k dielectric material to suppress undesired copper diffusion. Low-k dielectric materials, however, have characteristics that make it difficult to integrate them into existing integrated circuit structures and processes. Compared to the conventional silicon dioxide (SiO2), low-k materials, due to the inherent properties thereof, typically have disadvantages such as low mechanical strength, high moisture absorption, poor adhesion, and unstably stress levels and are easily damaged by fabrication processes such as etching, ashing and cleaning used in copper fabrication. In addition, low-k materials used in the copper fabrication are often formed with a certain porosity to reduce the dielectric constant thereof. Therefore, when an opening for forming an interconnect structure is defined in the low-k dielectric material, sidewalls with poor surface roughness are often formed, especially when the low-k materials are formed with a certain porosity for the purpose of reducing the dielectric constant thereof, thus causing poor adhesion between the low-k materials and the sequential formed metal barrier layer of a subsequently formed copper interconnect structure results and may affect reliability thereof.